Electronic Factors Controlling Bandwidths in Oxides with the Perovskite and Cadmium Halide Structures

Abstract

The electronic structure of oxides with the perovskite and cadmium halide structures are derived using tightbinding theory and the angular overlap model. The control of the form of the energy bands by the presence of vertex(perovskite) and edge-sharing (cadmium halide) of the coordination octahedra is first explored using onedimensional examples. For one-, two-, and three-dimensional structures of the perovskite type, a very interesting result is uncovered. It is shown that on the band model a band gap may only arise if the oxygen 2s orbital is included in the orbital problem. Prediction of the magnitude of the band gaps in d6 perovskites is thus not a simple matter. This band structure, derived from tight-binding theory via the construction of Bloch orbitals, is compared with an energy band scheme based on local crystal field orbitals and covalent metal-oxygen interactions, which has traditionally been used in this area.